Zinc electroplating



Patented Feb. 15, 1949 zmo ELECTROPLATING Allan E. Chester, Highland Park, and Frederick F. Reisinger, Waukegan, 111., assignors to Poor & Company, Chicago, 111., a corporation of Delaware 4 No Drawing. Application April 24, 1944,

Serial No. 532,533

14 Claims. 1

This invention relates to a new and useful zinc electroplating composition, and to a new and improved method for electrodepositing zinc.

One of the objects of the invention is to provide new and improved zinc electroplating baths.

Another object of the invention is to produce new and improved cyanide-zinc plating baths from which extraordinarily bright zinc deposits are produced by electrodeposition.

Another object of the invention is to provide a new and improved method for electrodepositing zinc. Other objects will appear hereinafter.

In accordance with the invention, it has been found that new and useful cyanide-zinc plating baths are obtained by incorporating with an alkaline cyanide-zinc plating bath a reaction product of piperonyl aldehyde and an aldonic acid, preferably gluconic acid. The reaction product is preferably formed in the presence of a lower fatty acid, such as for example acetic acid, which apparently acts as a catalyst and which may be allowed to remain in the final composition.

A further feature of the invention is the preparation of electroplating compositions of the type described in which the reaction product of piperonyl aldehyde and the aldonic acid is dissolved in organic solvents, as for example diethylene glycol monobutyl e t h e r (C4H9.O.CH2.CH2.O.CH2.CH2.OH) a l s known as butyl Carbitol, methyl "Cellosolve Formal (CH2(OCH2CH2OCH3)2) and ethyl Cellosolve Formal (CH2(OCH2CH2OC2H5)2) or other water miscible organic solvents. The organic solvent solutions of the aforesaid reaction products when added to aqueous alkaline baths, as for example alkaline zinc-cyanide electroplating baths, form emulsions which-break almost immediately into clear solutions. These solutions will readily pass through a filter, and the reaction products of the piperonyl aldehyde with the aldonic acid contained therein are not removed by the filtration. Since electroplating baths sometimes have to be filtered for the removal of impurities, the type of plating bath prepared as herein described is especially useful.

While alkaline zinc-cyanide plating baths are improved in certain respects by the incorporation of the aforesaid reaction products or organic solvent solutions thereof, the incorporation of these substances and the incorporation of gelatin-aldonic acid reaction products in the same plating bath produce extraordinary brightening effects in the electrodeposition of zinc fromcyanide baths. These unusual brightening effects are not obtained from either ingredient used individually.

The invention will be illustrated but is not limited by the following examples in which the quantities are stated in parts by weight unless otherwise indicated:

Example I This example illustrates the preparation of piperonyl aldehyde-aldonic acid reaction produc s.

Piperony' aldehyde (piperonal), a solution of 50% gluconic acid, and a solution of 91% acetic acid are mixed together in proportions within the following range:

Piperonyl aldehyde grams l-4.2 Gluconic acid (50% concentration) cc 10-18 Acetic acid (91% concentration) -cc 17- 9 Example II The acetic acid can be omitted in carrying out Example I, in which case, however, the heating of the piperonyl aldehyde with the gluconic acid is preferably continued for about 6 to 10 hours.

A product having similar properties is obtained which is soluble in butyl Carbitol and other similar water miscible organic solvents.

Example III This example illustrates the preparation of cyanide-zinc plating baths in accordance with the invention.

Electrolytes were prepared by mixing together certain ingredients as indicated under A, B, or

C below:

Sodium cyanide grams -100 Zinc metal (added as zinc oxide) "grams 36- 40 Sodium hydroxide grams -115 and enough water to make 1 liter of solution.

2 grams per liter of zinc dust was stirred into the electrolyte and the entire mixture was filtered in order to remove traces of heavy metals;

3 cc. to 60 cc. of the piperonyl aldehyde-aldonic acid composition of Example I were added to each gallon of said electrolyte and zinc was electrodeaeeaeoe pared as follows:

34 grams of gelatin were mixed with 100 cc. of 50% gluconic acid. The reaction mixture was digested from /2 to 1 hour at a temperature of from 80 to 120 F. The mixture was then stirred vigorously and the temperature gradually raised to 180 F. with the addition of 490 cc. of water.

C. An electrolyte was prepared as in B except that cc. of furfural were added to the gelatingluconic acid solution after it was heated to 180 F. and while it was still hot. The presence of the furfural enhances the smoothness of the zinc deposit. Otherwise, the results are similiar to those obtained under B.

Piperonyl aldehyde per se is insoluble in water and in alkaline zinc plating baths, whereas the aldonic derivatives thereof either form emulsions (when they are prepared without the organic solvent), or form emulsions which break to give clear solutions (when they are prepared with the organic solvent). Thus, when the compositions of Examples I or II are added to a cyanide-zinc plating bath, the emulsion forms and breaks immediately and the bath becomes a clear light yellow color. It can be filtered without taking out any of the reaction product.

In the preparation of any of the aldonic acid derivatives herein described other aldonic acids may be used instead of gluconic acid, as for example mannonic, arabonic, galactonic, and xylonic. All of these exist in alpha and beta lactone forms.

The invention is subject to certain other variations and modifications in the manner of its practical application; thus. in the reaction between the piperonyl aldehyde and the aldonic acid, somewhat higher temperatures may be used but care should be taken to avoid temperatures which are suificiently high to cause carmallizing. Other lower fatty acids may be employed as a catalyst. as for example propionic acid. If other acids are employed as catalysts and the products are to be ued in electroplating baths, care should be taken to avoid the use of acids that might have a harmful effect on the bath itself or upon the electroplating operation.

The gelatin-aldonic acid derivatives are described and claimed in our co-pending application Serial No. 525.323. filed March 6, 1944. now Patent No. 2,458,504. The piperonyl aldehyde-aldonic acid derivatives are described and claimed in our co-pending application Serial No. 532,532, filed April 24, 1944, now United States Patent No. 2,390,511.

One of the advantages of the invention is the provision of new and improved electrolytes containing new reaction products in much larger percentages than is possible with the parent substances from which these new reaction products are derived. This. in turn, produces new and improved results ln electroplating which can not be obtained with the parent substances. The invention provides a new, simple, and economical method for electrodepositing zinc which produces new and unusual results.

The invention is hereby claimed as follows:

1. A zinc plating bath comprising essentially an aqueous alkaline zinc-cyanide solution containing in solution about 3 cc. to about 60 cc. per gallon of bath of the reaction product of piperonyl aldehyde and gluconic acid reacted in proportions corresponding to approximately 1-4.2 grams of piperonyl aldehyde to 10-18 cc. of 50% gluconic acid in the presence of 17-9 cc. of 91% acetic acid, and then diluted with approximately 9 cc. to 27 cc. of diethylene glycol monobutyl ether.

2. A zinc plating composition comprising essentially an aqueous alkaline zinc-cyanide solution containing in solution the reaction product of piperonyl aldehyde with an aldonic acid and the reaction product of gelatin with an aldonic acid in proportions corresponding to approximately 3 cc. to 60 cc. per gallon of the piperonyl aldehyde-aldonic acid product and approximately 60-80 cc, per gallon of the gelatin-aldonic acid product.

3. The method of depositing zinc which coinprises electrodepositing zinc from an aqueous alkaline cyanide-zinc plating bath at current densities within the range of about 10 to about 50 amperes per square foot, in the presence of the bathsoluble reaction product of piperonyl aldehyde and gluconic acid incorporated in the bath in the form of a water miscible organic solvent solution thereof and in the presence of the bath-soluble'reaction product of gelatin and gluconic acid incorporated in the bath, in proportions within the range from about 3 cc. to about 60 cc. per gallon of electrolyte of said water miscible organic solvent solution of said reaction product, and approximately 60-80 cc. per gallon of electrolyte of said gelatingluconic acid reaction product.

4. A zinc plating composition comprising essentially an aqueous alkaline zinc-cyanide solution containing, dissolved in the solution, a sumcient amount of the product of the reaction of piperonyl aldehyde with an aldonic acid to enhance brightness.

5. A zinc plating composition comprising essentially an aqueous alkaline zinc-cyanide solution containing, dissolved in the solution, a sufllcient amount of the product of the reaction of piperonyl aldehyde, an aldonic acid, and a lower fatty acid, to enhance brightness.

6. A zinc plating composition comprising essentially an aqueous alkaline zinc-cyanide solution containing, dissolved in the solution, a sumcient amount of the product of the reaction of piperonyl aldehyde and gluconic acid to enhance brightness.

7. A zinc plating composition comprising essentially an aqueous alkaline zinc-cyanide solution containing, dissolved in the solution, a sufllcient amount of the product of the reaction of piperonyl aldehyde, gluconic acid, and acetic acid to enhance brightness.

8. A zinc plating composition comprising essentially an aqueous alkaline zinc-cyanide solution containing, dissolved in the solution, a sumcient amount of the product of the reaction of piperonyl aldehyde with an aldonic acid to enhance brightnes the said product being dissolved in a water miscible organic solvent.

9. A zinc plating bath comprising essentially an aqueous alkaline zinc-cyanide solution containing a composition comprising the reaction product of piperonyl aldehyde with an aldonic acid dissolved in a water miscible organic solvent, said composialkaline bath, forms an emulsion that breaks immediately and dissolves in said bath.

10. A-zlnc plating bath comprising essentially an aqueous alkaline zinc-cyanide solution containing suiiicient'amounts, dissolved in said bath, of the reaction product of piperonyl aldehyde with an aldonic acid and the reaction product of gelatin with an aldonic acid to enhance brightness. I 11. The method of depositing zinc which comprises electrodepositing zinc from an aqueous alkaline cyanide-zinc plating bath containing a sufficient amount of dissolved product of the reaction of piperonyl aldehyde and an aldonic acid to enhance brightness,

12. The method of depositing zinc which comprises electrodepositing zinc from an aqueous alkaline cyanide-zinc plating bath containing a suflicient amount of dissolved product of the reaction of piperonyl aldehyde with an aldonic acid and the product of the reaction of gelatin with an aldonic acid to enhance brightness.

13; The method of depositing zinc which comprises electrodepositing zinc from an aqueous a1 kaline cyanide-zinc plating bath containing a sufficient amount of dissolved product of the reaction of piperonyl aldehyde and gluconic acid to enhance brightness.

14. The method of depositing zinc which comprises electrodepositing zinc fron i an aqueous alkaline cyanide-zinc plating bath containing a sufficient amount of dissolved product of the reaction of piperonyl aldehyde with an aldonic acid and the product of the reaction of gelatin, an aldonic acid and furfural to enhance brightness.

ALLAN E. CHESTER. FREDERICK F. REISINGER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 694,658 Meurant Mar. 4, 1902 2,196,588 Hull Apr. 9, 1940 2,390,511 Chester et a1. Dec. 11, 1945 

